1. Field of the Invention
One or more embodiments of the present invention generally relate to seismic data processing, and more particularly to correcting seismic data from dissipative effects.
2. Description of the Related Art
In seismic exploration, seismic data are obtained by first creating an artificial disturbance along the earth by use of dynamite or the like. The resulting acoustic waves travel downwardly in the earth and are reflected upward from subsurface reflecting interfaces. The reflected waves are received at detectors or geophones located along the ground and recorded in reproducible form. Ideally, the signals recorded at the detectors would be exactly representative of the reflection characteristics of the earth without the presence of any undesirable components, such as noise or distortion.
Unfortunately, the signals recorded at the detectors often contain many undesirable components which obscure the reflectivity function of the earth and prevent the finding of an area of the earth where oil and gas deposits may be present. Several phenomena exist in causing distortion to the recorded signals. One such phenomenon is absorption, which causes the actual loss of seismic energy by converting it to other forms of energy. This type of loss of seismic energy is generally known as intrinsic attenuation. A second phenomenon is intrabed multiple interference. Intrabed multiple interference redistributes seismic energy between downward and upward directions. This type of loss of seismic energy is generally known as apparent attenuation. Apparent attenuation causes progressive loss of the higher frequencies (broadening of the seismic wavelet) and increasing phase distortion with increasing traveltime for the received seismic wavelet.
The combination of intrinsic and apparent attenuation is generally known as the earth filter. As a result of earth filtering, the seismic wavelet is time varying. The existence of a time varying seismic wavelet violates a basic assumption of deconvolution theory and impairs the ability to use deconvolution to determine the earth filter characteristics as part of a method of seismic interpretation.
One conventional approach to compensate for earth filter attenuation is disclosed in Q-Adaptive Deconvolution, by D. Hale, Stanford Exploration Project, Report 30, 1982. Hale discloses two iterative procedures for implementing inverse Q-filtering. The procedures disclosed by Hale make several assumptions which cause Hale to arrive at an approximate dispersion relationship. Use of the approximate dispersion relationship, however, degrades the value of the Q compensation obtained by Hale.
Further, application of zero offset inverse Q algorithm to prestack data (or data having non zero offsets) in the t−x domain often leads to insufficient compensation, because events having similar traveltimes may have experienced substantially different levels of attenuation along their raypaths. This phenomenon may be particularly true in deep water and at high offsets. In those situations, the reflection from the water bottom, which has experienced no attenuation, may coincide in arrival time with much deeper reflections that may have experienced significant attenuation. As such, a single Q filter may not be sufficient to accurately compensate for the reflections.
Therefore, a need exists in the art for a new method for correcting input seismic data from dissipative effects.